Segmental near nerve sensory conduction studies of the medical and lateral plantar nerve.

Tarsal Tunnel Syndrome (TTS) can be difficult to diagnose: electrophysiologic corroboration is important and has therapeutic implications. Conventional electrodiagnostic techniques are insensitive: motor latency abnormalities exist in only 52%; sensory responses are frequently absent (a nonlocalizing finding). Additionally, previously described near nerve techniques do not isolate conduction velocity (CV) measurement to the short segment across the flexor retinaculum (FR), which would theoretically improve sensitivity. We describe a technique which allows for the determination of segmental sensory CVs of the medial (MP) and lateral (LP) plantar nerves, both below (BFR) and across (AFR) the FR. Seventeen normal patients (age 22-45) were studied. Near nerve recording electrodes were positioned close to the specified nerve below and above the FR. Ring electrode stimulation (RES) of digits I (MP) or V (LP) and direct near nerve stimulation (NNS) BFR were performed. With RES digit I (n = 17), mean CV (toe to BFR) was 39.0 +/- 7.1 m/s; CV (AFR) 47.9 +/- 6.2 m/s. CV (AFR) following NNS (MP) (n = 16) was 49.4 +/- 5.1 m/s. With RES digit V (n = 10), mean CV (toe to BFR) was 36.4 +/- 3.4 m/s; CV (AFR) 57.5 +/- 6.9 m/s. CV (AFR) with NNS (LP) (n = 14) was 59.8 +/- 6.2 m/s. In conclusion, segmental MP and LP sensory CVs can be reliably obtained with near nerve technique. This approach may improve the diagnostic sensitivity of EMG in TTS.